The present invention relates to new crystalline silicate compositions. Further, this invention relates to methods for producing these new crystalline metal silicate compositions and to a method for the catalytic conversion of synthesis gas to low molecular weight hydrocarbons utilizing these compositions. 2. Discussion of the Prior Art
Zeolite materials, both natural and synthetic, are known to have catalytic capability for various types of reactions, especially hydrocarbon conversions. The well known crystalline aluminosilicate zeolites are commonly referred to as "molecular sieves" and are characterized by their highly ordered crystalline structure and uniformly dimensioned pores, and are distinguishable from each other on the basis of composition, crystal structure, adsorption properties and the like. The term "molecular sieves" is derived from the ability of the zeolite materials to selectively adsorb molecules on the basis of their size and form.
The processes for producing such crystalline synthetic zeolites are well known in the art. A family of crystalline aluminosilicate zeolites, designated ZSM-5, is disclosed in U.S. Pat. No. 3,702,886, said patent being herein incorporated by reference.
U.S. Pat. No. 3,941,871 relates to novel crystalline metal organosilicates which are essentially free of Group IIIA metals, i.e., aluminum and/or gallium. This patent is herein incorporated by reference. It is noted therein that the amount of alumina present in the known zeolites appears directly related to the acidity characteristics of the resultant product and that a low alumina content has been recognized as being advantageous in attaining a low degree of acidity which in many catalytic reactions is translated into low coke making properties and low aging rates. A typical procedure for making the organosilicates is to react a mixture containing a tetraalkylammonium compound, sodium hydroxide, an oxide of a metal other than a metal of Group IIIA, an oxide of silicon, and water until crystals of said metal organosilicates are formed. It is also noted in the patent that the family of crystalline metal organosilicates have a definite X-ray diffraction pattern which is similar to that for the ZSM-5 zeolites. Minor amounts of alumina are contemplated in the patent and are attributable primarily to the presence of aluminum impurities in the reactants and/or equipment employed.
U.S. Pat. No. 3,884,835 discloses crystalline silica compositions. The crystalline silica materials may also contain a metal promoter which may be selected from Group IIIA, Group VB or Group VIB elements. Boron is disclosed as one of the metal promoters.
U.S Pat. No. 4,088,605 is directed to the synthesis of a zeolite, such as ZSM-5, which contains an outer shell free from aluminum. The patent states at column 10, the paragraph beginning at line 20, that to produce the outer aluminum-free shell, it is also essential that the reactive aluminum be removed from the reaction mixture. It is therefore necessary, as noted therein, to process the zeolite and to replace the crystallization medium with an aluminum-free mixture to obtain crystallization of SiO.sub.2 on the surface of the zeolite which can be accomplished by a total replacement of the reaction mixture or by complexing from the original reaction mixture any remaining aluminum ion with reagents such as gluconic acid or ethylenediaminotetraacetic acid (EDTA).
Crystalline borosilicate compositions are disclosed in German Offenlegungschrift No. 2,746,790. This application relates specifically to borosilicates which are prepared using the usual procedures for making the aluminosilicate zeolites. It is noted therein that in instances where a deliberate effort is made to eliminate aluminum from the borosilicate crystal structure because of its adverse influence on particular conversion processes, the molar ratios of SiO.sub.2 /Al.sub.2 O.sub.3 can easily exceed 2000-3000 and that this ratio is generally only limited by the availability of aluminum-free raw materials.
German Offenlegungschrift No. 2,755,770 (corresponding British Pat. No. 1,555,928), discloses the preparation of crystalline iron silicates with and without added aluminum, and discloses their use as catalysts for the conversion of methanol to hydrocarbons at high aromatic selectivity. It is further claimed that promoter such as boron can be added to these iron silicates, but no examples of such are given.
U S. Pat. No. 4,468,474 discloses hydrogen activated catalyst compositions comprising iron, silicon and carbon that selectively convert gaseous mixtures to C.sub.2 -C.sub.6 alkanes. It is further noted that the catalysts maintained their activity and high selectivity over a long period and that regeneration of partially deactivated catalysts can be accomplished by treatment with hydrogen at elevated temperature.
U.S. Pat. No. 4,298,695 discloses the conversion of synthesis gas to a liquid hydrocarbon, i.e. naphtha. The process does not employ catalysts which need promoters. High activity without aging is characteristic of the process.
U.S. Pat. No. 4,418,155 discloses a process for the conversion of synthesis gas utilizing a catalyst which comprises a ZSM-5 type zeolite and a carbon oxide reducing component. This process yields a particular product, i.e. linear alpha-olefins, (C.sub.4 -C.sub.6 olefins).
While the art has provided zeolitic catalysts having a wide variety of catalytic and adsorbtive properties, the need still exists for crystalline materials having different and/or enhanced catalytic properties. For example, an important use for a catalytic material is the conversion of synthesis gas to low molecular weight hydrocarbons. Further, many hydrocarbon conversion processes are performed employing zeolites, i.e. alkylation and isomerization. As is well-known in the art, it is important to maximize selectivity for a desired product.
Accordingly, it is one object of the present invention to provide novel crystalline metal silicate compositions.
Another object of this invention is to provide novel crystalline ferrometallosilicate compositions having different and enhanced catalytic properties.
A further object of the invention herein is to provide a method for the preparation of these novel crystalline ferrometallosilicate compositions.
A still further object of this invention is to provide an improved method for the conversion of hydrocarbons and oxygenated compounds to selected end products.
Still another object of this invention is to provide an improved method for the conversion of synthesis gas to low molecular weight hydrocarbons utilizing ferrometallosilicate compositions.
The achievement of these and other objects will be apparent from the following description of the subject invention.